Cancer remains one of the most severe health problems in America, accounting for substantial fatality and health costs in society. Tumorigenesis in humans is a complex process involving activation of oncogenes and inactivation of tumor suppressor genes (Bishop, 1991, Cell 64:235-248). Tumor suppressor genes in humans have been identified through studies of genetic changes occurring in cancer cells (Ponder, 1990, Trends Genet. 6:213-218; Weinberg, 1991, Science 254:1138-1146).
There is a close association between particular chromosomal abnormalities, e.g., chromosomal translocations, inversions, and deletions, and certain types of malignancy, indicating that such abnormalities may have a causative role in the cancer process. Chromosomal abnormalities may lead to gene fusion resulting in chimeric oncoproteins, such as is observed in the majority of the tumors involving the myeloid lineage. Alternatively, chromosomal abnormalities may lead to deregulation of protooncogenes by their juxtaposition to a regulatory element active in the hematopoietic cells, such as is observed in the translocation occurring in the lymphocytic lineage (Virgilio et al., 1993, Proc. Natl. Acad. Sci. USA 90:9275-9279). Deletions may cause loss of tumor suppressor genes, leading to malignancy.
Nonrandom chromosomal translocations are characteristic of most human hematopoietic malignancies (Haluska et al., 1987, Ann. Rev. Genet. 21:321-345) and may be involved in some solid tumors (Croce, 1987, Cell 49:155-156). In B and T cells, chromosomal translocations and inversions often occur as a consequence of mistakes during the normal process of recombination of the genes for immunoglobulins (Ig) or T-cell receptors (TCR). These rearrangements juxtapose enhancer elements of the Ig or TCR genes to oncogenes whose expression is then deregulated (Croce, 1987, Cell 49:155-156). In the majority of the cases, the rearrangements observed in lymphoid malignancies occur between two different chromosomes.
The TCL-1 locus on chromosome 14 band q32.1 is frequently involved in the chromosomal translocations and inversions with the T-cell receptor genes observed in several post-thymic types of T-cell leukemias and lymphomas, including T-prolymphocytic leukemias (T-PLL) (Brito-Babapulle and Catovsky, 1991, Cancer Genet. Cytogenet. 55:1-9), acute and chronic leukemias associated with the immunodeficiency syndrome ataxia-telangiectasia (AT) (Russo et al., 1988, Cell 53:137-144; Russo et al., 1989, Proc. Natl. Acad. Sci. USA 86:602-606), and adult T-cell leukemia (Virgilio et al., 1993, Proc. Natl. Acad. Sci. USA 90:9275-9279).
In 1979, a large Italian-American family in Boston was observed to be transmitting a constitutional reciprocal t(3;8)(p14.2;q24) chromosome translocation (Cohen et al., 1979, N. Engl. J. Med. 301:592-595; Wang and Perkins, 1984, Cancer Genet. Cytogenet. 11:479-481) which segregated in the family with early onset, bilateral and multifocal clear cell renal carcinoma (RCC). Follow-up cytogenetic studies in several familial tumors demonstrated that the tumors had lost the derivative 8 chromosome carrying the translocated 3p14-pter region; consequently, the tumors were homozygous for all loci telomeric to the 3p14.2 break (Li et al., 1993, Annals of Internal Medicine 118:106-111). It was suggested that the translocation affects expression of a tumor suppressor gene (Cohen et al., 1979, N. Engl. J. Med. 301:592-595) and several investigators have sought candidate suppressor genes. We had suggested the protein tyrosine phosphatase gamma gene (PTPRG) as a candidate tumor suppressor gene (LaForgia et al., 1991, Proc. Natl. Acad. Sci. USA 88:5036-5040), and that the majority of clear cell RCCs exhibit loss of heterozygosity of a 0.5 Mb region flanking the translocation (Lubinski et al., 1994, Cancer Res. 54:3710-3713; Druck et al., 1995, Cancer Res. 55:5348-5355), although we did not observe aberrations in the remaining PTPRG gene. The 3p14.2 region is also included in deletions in numerous other tumor types, including nasopharyngeal carcinomas (Lo et al., 1994, Int. J. Oncol. 4:1359-1364).
The t(3;8) translocation breakpoint was cloned and a 3 kb transcript of a candidate tumor suppressor gene was detected using a probe from near the breakpoint (Boldog et al., 1993, Proc. Natl. Acad. Sci. USA 90:8509-8513); further details concerning this transcript have not been reported in spite of a later publication from this group relating to this subject, and reporting a YAC contig of approximately 6 Mb DNA spanning the 3p14.2 3;8 translocation breakpoint (Boldog et al., 1994, Genes, Chromosomes & Cancer 11:216-221). It has also been suggested that there may not be a suppressor gene at 3p14.2, that in fact the t(3;8) translocation was a mechanism for losing the von Hippel-Lindau gene, a tumor suppressor gene at 3p25 (Gnarra et al., 1994, Nature Genet. 7:85-90).
Another cytogenetic landmark in chromosome region 3p14.2 is the most common of the constitutive aphidicolin inducible fragile sites, FRA3B, which is cytogenetically indistinguishable from the t(3;8) translocation (Glover et al., 1988, Cancer Genet. Cytogenet. 31:69-73). Fragile sites, of which over 100 have been described in human (for review, see Sutherland, 1991, Genet. Anal. Tech. Appl. 8:1616-166), are regions of the human genome which reveal cytogenetically detectable gaps when exposed to specific reagents or culture conditions; several folate sensitive, heritable, X-linked and autosomal fragile sites have been localized to unstable CCG or CGG repeats (Yu et al., 1991, Science 252:1179-1181; Kremer et al., 1991, Science 252, 1711-1714; Verkerk et al., 1991, Cell 65:905-914; Fu et al., 1991, Cell 67:1047-1058), and for one of these, the FRA11B at 11q23.3, the CCG repeat is within the 5' untranslated region of the CBL2 gene, a known protooncogene (Jones et al., 1995, Nature 376:145-149). Also this fragile site, FRA11B, is associated with Jacobsen (11q-) syndrome, showing a direct link between a fragile site and in vivo chromosome breakage (Jones et al., 1994, Hum. Mol. Genet. 3:2123-2130). Because the induced fragile sites resemble gaps or breaks in chromosomes, it has frequently been speculated that fragile sites could be sites of chromosomal rearrangement in cancer (Yunis and Soreng, 1984, Science 226:1199-1204).
Previously identified fragile sites have also been shown to be hypermethylated (Knight et al., 1993, Cell 74:127-134); thus methylation of a fragile site in a tumor suppressor gene regulatory region might cause loss of transcription of the suppressor gene, serving as one "hit" in the tumorigenic process, as pointed out previously (Jones et al., 1995, Nature 376:145-149). These authors also suggested that an important contribution of fragile site expression in tumorigenesis might be to increase the incidence of chromosome deletion during tumorigenesis.
The FRA3B region has been delineated by studies of several groups using rodent-human hybrids; hybrid cells retaining human chromosome 3 or 3 and X, on a hamster background, were treated with aphidicolin or 6-thioguanine (t select hybrids which had lost the X chromosome) and subclones selected. Subclones retaining portions of chromosome 3 with apparent breaks in region 3p14-p21 were characterized for loss or retention of specific 3p markers to determine the position of 3p14-21 breaks (LaForgia et al., 1991, Proc. Natl. Acad. Sci. USA 88:5036-5040, LaForgia et al., 1993, Cancer Res. 53:3118-3124; Paradee et al., 1995, Genomics 27:358-361).
There remains an unfulfilled need to isolate and characterize the genes associated with digestive tract and other cancers for use as a diagnostic and therapeutic/prophylactic reagent in the detection, treatment, and prevention of such cancers.
Citation of a reference hereinabove shall not be construed as an admission that such reference is prior art to the present invention.